Transcript

2.
1. Waterfalls are often formed where a layer of
harder rock overlays a layer of softer rock.
Harder rock
Softer rock

3.
2. As the river passes over the softer rock, it is able to
erode it at a faster rate, forming a step in the river bed.
Harder rock
Softer rock

4.
Harder rock
Softer rock
ii. it undercuts
the harder rock
to form a notch
3. The force of hydraulic
action does two things:
i. deepens the step to
form a plunge pool at
the base of the waterfall
Further erosion makes the plunge pool and notch bigger over time.

5.
Harder rock
Softer rock
As the notch grows,
eventually there isn’t
enough support under
the harder rock and so
it collapses into the
plunge pool.

6.
Harder rock
Softer rock
This adds rocks and boulders
to the plunge pool, and so the
process of corrasion works
with hydraulic action to
further erode the plunge pool
and notch.

7.
Harder rock
Softer rock
The processes of erosion
continue, further eroding out
the notch and plunge pool.
Eventually the harder rock
above will collapse again,
meaning that the waterfall will
retreat upstream over time.